To present a case in which even the coarsest WKB
approximation (REF ) cannot readily be obtained
without continuum methods, Fig. REF  shows a CRN known
as the Selkov model, which was treated with eikonal methods by Dykman
et al. [1]}. The Selkov model is an
asymmetric autocatalytic system for which we can choose fixed points
and residence times similar to those in the cross-catalytic CRN,
though the eikonals in the two models show qualitative differences.
<FIGURE>